CASPASE-MEDIATED CLEAVAGE OF FOCAL ADHESION KINASE PP125(FAK) AND DISASSEMBLY OF FOCAL ADHESIONS IN HUMAN ENDOTHELIAL-CELL APOPTOSIS

Normal endothelial and epithelial cells undergo apoptosis when cell ad hesion and spreading are prevented, implying a requirement for antiapo ptotic signals from the extracellular matrix for cell survival. We inv estigated some of the molecular changes occurring in focal adhesions d uring growth factor deprivation-induced apoptosis in confluent monolay ers of human umbilical vein endothelial cells. Among the first morphol ogic changes after initiation of the apoptotic process are membrane bl ebbing, loss of focal adhesion sites, and retraction from the matrix f ollowed by detachment. We observe a specific proteolytic cleavage of f ocal adhesion kinase (pp125(FAK)), an important component of the focal adhesion complex, and identify pp125(FAK) as a novel substrate for ca spase-3 and caspase-3-like apoptotic caspases. The initial cleavage pr ecedes detachment, and coincides with loss of pp125(FAK) and paxillin from focal adhesion sites and their redistribution into the characteri stic membrane blebs of apoptotically dying cells. Cleavage of pp125(FA K) differentially affects its association with signaling and cytoskele tal components of the focal adhesion complex; binding of paxillin, hut not pp130(Cas) (Cas, Crk-associated substrate) and vinculin, to the C OOH terminally truncated pp125(FAK) is abolished. Therefore, caspase-m ediated cleavage of pp125(FAK) may be participating in the disassembly of the focal adhesion complex and actively interrupting survival sign als from the extracellular matrix, thus propagating the cell death pro gram.